Laser photocoagulation of the trabecular meshwork has proven clinically useful in treatment of several forms of open-angle glaucoma. Currently this therapy is considered an attractive alternative to incisional surgery when medical therapy fails. Furthermore, there is increasing interest in laser trabeculoplasty as an alternative even to successful medical therapy since it offers the potential for a one time intervention which is generalliy effective and long lasting. Despite its widespread clnical use, the effects of laser trabeculoplasty remain poorly understood in several fundamental ways. It has been suggested that laser trabeculoplasty works by tightening trabecular tissue and thereby relieving trabecular resistance; this theory remains a largely unproven hypothesis. Though generally considered to have a low incidence of serious side effects, potentially hazardous elevations of pressure frequently occur in the period immediately following therapy and the mechanism for this reaction remains unclear. And though no disastrous sequelae have been reported in the presently available follow-up period of approximately five years, the long-term safety of this treatment is not yet proven. We propose a laboratory study in which the effects of laser trabeculoplasty will be assessed using correlated evaluations of aqueous outflow function and structure. Functional aspects of aqueous outflow will be determined in two ways: by measuring the facility of aqueous outflow using in vivo quantitative perfusion and by mapping the microscopic pathways of flow using a tracer substance. These data will be analyzed as a function of time and of variations in treatment. In addition, the functional measurements will be correlated with detailed analysis of morphologic alterations in tissues as they are observed using light and electron (both scanning and transmission) microscopy.